Studies on the detailed biology of most of the indigenous fishes from India are lacking including species of the genus Balitora and genus Psilorhynchus though a total of 21 and 28 species respectively has been described so far (Froese and Pauly, 08 / 2019). This study on the reproductive biology of B. brucei and P. balitora will be able to fill this gap.
Sexual dimorphism is not very prominent in a number of fishes. For those, abdominal dissection is the only way to confirm the sex. Sex differentiation in B. brucei and P. balitora was not easy in the field (Conway, 2011; Conway et al., 2014) due to absence of remarkable visible character on the specimen. To analyze the presence of any sexually dimorphic character statistically, a homogeneity test (Mann Whitney U test) was performed with the data recorded on 20 males and 20 female specimens. It was found that body depth in the anal region of the gravid female fishes of B. brucei and wider body in the anal region of the gravid female fishes of P. balitora showing sexual dimorphism during breeding. Applying this homogenity test, Bordoloi and Baishya (2006) analyzed the sexual dimorphism for Puntius ornatus and recorded the differences in body width, interorbital space and in the length of caudal peduncle between the sexes. Later, Bordoloi and Saha (2007) did a comparative study in Clupisoma montana, Clupisoma garua and Eutropiichthys vacha using the same homogeneity test. Conway, 2011 on the other hand studied the osteology of the genus Psilorhynchus and found that the architecture of the Weberian apparatus shows sexual dimorphism. Later Conway et al., 2014 again found that the structure of the swimbladder also exhibits sexual dimorphism in the Psilorhynchid fishes.
The populations of B. brucei and P. balitora showed an unbalanced sex ratio in Ranganadi River with females outnumbering and attaining larger size than in males. This difference in sex ratio could be due to various reasons like the sex growth rate, behavior and mortality (Gomes et al., 2011). But the ecological importance of sex ratio is still not fully explained (Gross, 2005).
Condition factor (K) and the relative condition (Kn) factor are the two important parameters of fish biology analysis that used to study the recent physical and biological circumstances and fluctuations due to interactions among feeding conditions, parasitic infections, physiological factors and to compare the condition within a given sample (Le Cren, 1951). The condition factor also reflects food availability and growth, but is variable and dynamic. Schneider et al., 2000, found that individual fish within the same sample may differ considerably, and the average condition of each population varies seasonally and yearly. In the current study, the K value in male and female fishes of both B. brucei and P. balitora shows different values (B. brucei, 0.729 ± 0.04 for males and 0.772 ± 0.048 for females; P. balitora, 1.000 ± 0.0229 in male and 1.035 ± 0.027 in female). A similar result on different ‘K’ values between the sexes of two Cyprinids; Rasbora tawarensis and Poropuntius tawarensis from Indonesia was obtained by Muchlisin et al., 2010. It was observed that the “K” value for B. brucei < 1 and for P. balitora is > 1. The ‘K’ values of P. balitora (in both the sexes) were higher than 1 indicating habitat suitability for the growth of the fish (George et al., 1985). Similar study by Barnham and Baxter, 1998 supports our findings. As per their opinion, K value might be influenced by the age of fish, sex, season, stages of maturation, the fullness of gut, type of food consumed, the amount of fat reserve and degree of muscular development. Analysis of relative condition (Kn) factor for B. brucei males show peak in July (1.081 ± 0.01) and in April (1.01 ± 0.02) in case of females. While in P. balitora, the maximum Kn (1.01 ± 0.01) was recorded in May for male and April (1.005) for females. Our study supports the findings of George et al., 1985 who opines that if the value of the relative condition factor is more than 1; it indicates the general wellbeing of the fish. Our finding signifies that the habitat Ranganadi River is conducive for the growth of these two fishes.
Analyses of length-weight and length-length relationships of both the fishes show positive allometric growth with highly significant value, P < 0.001 (Kaushik and Bordoloi, 2017). In the present collection, the new maximum total length (TL = 81mm) has been recorded for P. balitora.
The size at first maturity gives the average total length of a fish species in which 50% of the fishes attain the sexual maturity. It is well known that the maturity of a fish varies considerably among different populations of the same species, different species and also within the limit of a single population (Nikolskii, 1963; Hossain et al., 2012). In the case of B. brucei,size at first maturity was recorded as 54 mm for males and 64.2 mm for females. While in P. balitora, the size at first maturity for males was 51 mm and for females was 58.6 mm.The data on size at first maturity exhibited that males attain maturity at a smaller size than the females. Similar results were obtained by Weyl and Booth, 1999 for the cyprinid fish Labeo cylindricus. Hossain et al., 2016 also obtained similar results for eight exotic species of Bangladesh.
A number of indices were used for assessing the reproductive pattern of a species. Gonado-somatic index (GSI) is known as the indicator of physiological activities of the gonads (Wang et al., 2013). The present study was based on macroscopic observation of the gonads, recording diameter of the oocyte and later confirmed with histological study. GSI revealed that the spawning mainly occurs from April to August in B. brucei and from November to March and July to August in P. balitora. It was observed that B. brucei prefers to breed in high water level and during rainfall. Moreover from April to August, there is rise in atmospheric as well as water temperature being monsoon as well as summer season. The peaks of GSI and K indicate an allocation of energy to somatic growth and reproduction (Gomes and Araujo, 2004). The minimum K was observed just after the spawning, when the fishes were heading to another spawning season. These kind of seasonal changes in K with minimum values recorded just after the spawning were observed by various fishery scientists (Bengtsson, 1993; Gomes et al., 2011). The GSI values recorded in females were higher than males signifying the seasonal development of gonads in the fish is more pronounced in females than in males. This kind of prolonged reproductive period was recorded for a loach Cobitis keyvani from Talar River of southern Caspian Sea basin by Mousavi et al., 2012. A similar study by Tsikliras et al., 2013 explained the monthly proportion of maturity stages for each sex which can be used as an indicator of the spawning season.
Estimation of fecundity is an indicator of the reproductive potential of the species. In the current investigation, both absolute fecundity (14320 ± 2316) and relative fecundity (3027 ± 402) for B. brucei was found to be higher than P. balitora (2537.70 ± 1705.9 and 822.43 ± 397.1). For this difference of range in fecundity, Bagenal, 1978 and Bagenal and Braum, 1978 stated that fecundity might vary among individuals of the same size and age.
Analysis of the sex ratio is very important from the conservation perspective. In the present study, the sex ratio of both B. brucei and P. balitora showed a significant deviation from 1:1, i.e. more males compared to the females. Dominance of males in most months was also reported in the Bengal loach Botia dario by Hussain et al., 2007 from Bangladesh and Das and Bordoloi, 2015 from Assam, India.
During the study a good number of samples were seen during monsoon season; which is the main breeding period for both the species reflecting the sampling sites as a breeding ground. But in the winter, a very less number were observed in the collections which reflect their local migratory behaviour from upstream to downstream during breeding period.
It was recorded during the period of investigation that local people use different types of fishing gears to catch the fishes from the river. As both the fishes are small in size, so their value as food fish is very less. As they inhabit running water with a high dissolved oxygen (DO), they are not suitable as ornamental fish.
Due to ecological and anthropogenic stress the number of these fishes are declining in natural habitats. It was found that local people use various fishing gears that result in eradication of non target species. Moreover techniques like electric fishing and use of chemicals for catching food fishes cause decline in small indigenous fishes that are not preferred food fishes. They also use the mixture of the leaf extract of Polygonum species, popularly known as “maanch” which is a piscicidal plant. During winter, when the water level goes down, this plant extract is applied in the downstream water that causes lowering of DO and eventually fishes acclimatized in high DO level float due to asphyxiation and they are collected.
A number of studies have mentioned the effect of dam in decline of indigenous fishes (Kingsford, 2001; Light and Marchetti, 2007; Mohite and Samant, 2013; and Sarkar et al., 2015). Periodic release of water by North Eastern Electric Power Corporation Limited (NEEPCO) was also recorded as a reason for the declining number of fishes in the Ranganadi river. During the release, water velocity forces the indigenous fishes to move along thereby causing instantaneous death and also there is adverse impact on the feeding and breeding of the surviving population.